Filter media formed from sheets of ceramic fibers, per se, are known in the art, as is the use of such ceramic-based media in filters for extraction of volatizable particulate material from gas streams, such as the exhaust from diesel engines. One such filter media and filter formed therefrom is disclosed in U.S. Pat. No. 5,087,272, including a method of manufacturing the ceramic-based medium itself. This patent is incorporated herein in its entirety by reference. Regeneration of filters which include a ceramic-based filter medium, employing microwave energy, is also disclosed in the prior art.
Known prior art ceramic-based filter media suffer from major problems, including, the inability to economically produce a web of ceramic fibers which is sufficiently pliable as permits the web to be folded, as by pleating employing small radii folds, into a geometry which is suitable for use in a filter unit where closely packed pleats are required due to size limitations imposed by the environment in which the filter is to be employed, the excessive steps, hence cost, required in the prior art to achieve a web of even limited pliability, and the inability to satisfactorily control the initial permeability and ensure the continued stability of the initial permeability of the prior art ceramic-fiber-based webs, leading to the tendency of the pores of the prior art filter media to become clogged by the particulate material which the filter extracts from an ambient environment. For example, current technology employs organic thermosetting binders to hold the shapes of the pleats of the web, and, after pleating of the web, the organic binder detracts from the high temperature performance of the pleated web and interferes with the subsequent addition of higher temperature inorganic binders to the web.